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P53
p53 (also known as protein 53 or tumor protein 53), is a tumor suppressor protein that in humans is encoded by the TP53 gene. p53 is crucial in multicellular organisms, where it regulates the cell cycle and, thus, functions as a tumor suppressor that is involved in preventing cancer. As such, p53 has been described as "the guardian of the genome" because of its role in conserving stability by preventing genome mutation. The name p53 is in reference to its apparent molecular mass: It runs as a 53-kilodalton (kDa) protein on SDS-PAGE. But, based on calculations from its amino acid residues, p53's mass is actually only 43.7 kDa. This difference is due to the high number of proline residues in the protein, which slows its migration on SDS-PAGE, thus making it appear heavier than it actually is. This effect is observed with p53 from a variety of species, including humans, rodents, frogs, and fish. Nomenclature p53 is also known as: * UniProt name: Cellular tumor antigen p53 * Antigen NY-CO-13 * Phosphoprotein p53 * Transformation-related protein 53 (TRP53) * Tumor suppressor p53 Gene In humans, p53 is encoded by the TP53 gene located on the short arm of chromosome 17 (17p13.1). The gene spans 20 kb, with a non-coding exon 1 and a very long first intron of 10 kb.The coding sequence contains five regions showing a high degree of conservation in vertebrates, predominantly in exons 2, 5, 6, 7 and 8, but the sequences found in invertebrates show only distant resemblance to mammalian TP53. TP53 orthologs have been identified in most mammals for which complete genome data are available. In humans, a common polymorphism involves the substitution of an arginine for a proline at codon position 72. Many studies have investigated a genetic link between this variation and cancer susceptibility, however, the results have been controversial. For instance, a meta-analysis from 2009 failed to show a link for cervical cancer. A 2011 study found that the TP53 proline mutation did have a profound effect on pancreatic cancer risk among males. A study of Arab women found that proline homozygosity at TP53 codon 72 is associated with a decreased risk for breast cancer. One study suggested that TP53 codon 72 polymorphisms, MDM2 SNP309, and A2164G may collectively be associated with non-oropharyngeal cancer susceptibility and that MDM2 SNP309 in combination with TP53 codon 72 may accelerate the development of non-oropharyngeal cancer in women. A 2011 study found that TP53 codon 72 polymorphism was associated with an increased risk of lung cancer. Meta-analyses from 2011 found no significant associations between TP53 codon 72 polymorphisms and both colorectal cancer risk and endometrial cancer risk. A 2011 study of a Brazilian birth cohort found an association between the non mutant arginine TP53 and individuals without a family history of cancer. Another 2011 study found that the p53 homozygous (Pro/Pro) genotype was associated with a significantly increased risk for renal cell carcinoma. (Italics are used to denote the TP53 gene name and distinguish it from the protein it encodes.) Structure Human p53 is 393 amino acids long and has seven domains: # an acidic N-terminus transcription-activation domain (TAD), also known as activation domain 1 (AD1), which activates transcription factors: residues 1-42. The N-terminus contains two complementary transcriptional activation domains, with a major one at residues 1–42 and a minor one at residues 55–75, specifically involved in the regulation of several pro-apoptotic genes. # activation domain 2 (AD2) important for apoptotic activity: residues 43-63. # Proline rich domain important for the apoptotic activity of p53: residues 64-92. # central DNA-binding core domain (DBD). Contains one zinc atom and several arginine amino acids: residues 102-292. This region is responsible for binding the p53 co-repressor LMO3. # nuclear localization signaling domain, residues 316-325. # homo-oligomerisation domain (OD): residues 307-355. Tetramerization is essential for the activity of p53 in vivo. # C-terminal involved in downregulation of DNA binding of the central domain: residues 356-393. A tandem of nine-amino-acid transactivation domains (9aaTAD) was identified in the AD1 and AD2 regions of transcription factor p53. KO mutations and position for p53 interaction with TFIID are listed below: ; ; ; ; 9aaTADs mediate p53 interaction with general coactivators - TAF9, CBP/p300 (all four domains KIX, TAZ1, TAZ2 and IBiD), GCN5 and PC4, regulatory protein MDM2 and replication protein A (RPA). ; ; ; The prediction for 9aaTADs (for both acidic and hydrophilic transactivation domains) is available online from ExPASy http://us.expasy.org/tools/ and EMBnet Spain http://www.es.embnet.org/Services/EMBnetAT/htdoc/9aatad/ Mutations that deactivate p53 in cancer usually occur in the DBD. Most of these mutations destroy the ability of the protein to bind to its target DNA sequences, and thus prevents transcriptional activation of these genes. As such, mutations in the DBD are recessive loss-of-function mutations. Molecules of p53 with mutations in the OD dimerise with wild-type p53, and prevent them from activating transcription. Therefore OD mutations have a dominant negative effect on the function of p53. An example of a mutation in P53 is where arginine 248 is altered, sometimes causing a disruption in balance and making the protein unable to bind with the DNA. Wild-type p53 is a labile protein, comprising folded and unstructured regions that function in a synergistic manner. Function p53 has many mechanisms of anticancer function, and plays a role in apoptosis, genomic stability, and inhibition of angiogenesis. In its anti-cancer role, p53 works through several mechanisms: * It can activate DNA repair proteins when DNA has sustained damage. * It can induce growth arrest by holding the cell cycle at the G1/S regulation point on DNA damage recognition (if it holds the cell here for long enough, the DNA repair proteins will have time to fix the damage and the cell will be allowed to continue the cell cycle). * It can initiate apoptosis, the programmed cell death, if DNA damage proves to be irreparable. Activated p53 binds DNA and activates expression of several genes including microRNA miR-34a, WAF1/CIP1 encoding for p21 and hundreds of other down-stream genes. p21 (WAF1) binds to the G1-S/CDK (CDK2) and S/CDK complexes (molecules important for the G1/S transition in the cell cycle) inhibiting their activity. When p21(WAF1) is complexed with CDK2 the cell cannot continue to the next stage of cell division. A mutant p53 will no longer bind DNA in an effective way, and, as a consequence, the p21 protein will not be available to act as the "stop signal" for cell division. Studies of human embryonic stem cells (hESCs) commonly describe the nonfunctional p53-p21 axis of the G1/S checkpoint pathway with subsequent relevance for cell cycle regulation and the DNA damage response (DDR). Importantly, p21 mRNA is clearly present and upregulated after the DDR in hESCs, but p21 protein is not detectable. In this cell type, p53 activates numerous microRNAs (like miR-302a, miR-302b, miR-302c, and miR-302d) that directly inhibit the p21 expression in hESCs. Recent research has also linked the p53 and RB1 pathways, via p14ARF, raising the possibility that the pathways may regulate each other. p53 by regulating LIF has been shown to facilitate implantation in the mouse model and possibly in humans. p53 expression can be stimulated by UV light, which also causes DNA damage. In this case, p53 can initiate events leading to tanning. Regulation p53 becomes activated in response to a myriad of stress types, which include but are not limited to DNA damage (induced by either UV, IR, or chemical agents such as hydrogen peroxide), oxidative stress, osmotic shock, ribonucleotide depletion, and deregulated oncogene expression. This activation is marked by two major events. First, the half-life of the p53 protein is increased drastically, leading to a quick accumulation of p53 in stressed cells. Second, a conformational change forces p53 to be activated as a transcription regulator in these cells. The critical event leading to the activation of p53 is the phosphorylation of its N-terminal domain. The N-terminal transcriptional activation domain contains a large number of phosphorylation sites and can be considered as the primary target for protein kinases transducing stress signals. The protein kinases that are known to target this transcriptional activation domain of p53 can be roughly divided into two groups. A first group of protein kinases belongs to the MAPK family (JNK1-3, ERK1-2, p38 MAPK), which is known to respond to several types of stress, such as membrane damage, oxidative stress, osmotic shock, heat shock, etc. A second group of protein kinases (ATR, ATM, CHK1 and CHK2, DNA-PK, CAK, TP53RK) is implicated in the genome integrity checkpoint, a molecular cascade that detects and responds to several forms of DNA damage caused by genotoxic stress. Oncogenes also stimulate p53 activation, mediated by the protein p14ARF. In unstressed cells, p53 levels are kept low through a continuous degradation of p53. A protein called Mdm2 (also called HDM2 in humans), which is itself a product of p53, binds to p53, preventing its action and transports it from the nucleus to the cytosol. Also Mdm2 acts as ubiquitin ligase and covalently attaches ubiquitin to p53 and thus marks p53 for degradation by the proteasome. However, ubiquitylation of p53 is reversible. A ubiquitin specific protease, USP7 (or HAUSP), can cleave ubiquitin off p53, thereby protecting it from proteasome-dependent degradation. This is one means by which p53 is stabilized in response to oncogenic insults. USP42 has also been shown to deubiquitinate p53 and may be required for the ability of p53 to respond to stress. Recent research has shown that HAUSP is a mainly localized in the nucleus, though a fraction of it can be found in the cytoplasm and mitochondria. Over expression of HAUSP results in p53 stabilization. However, depletion of HAUSP does not result to a decrease in p53 levels but rather increases p53 levels due to the fact that HAUSP binds and deubiquitinates Mdm2. It has been shown that HAUSP is a better binding partner to Mdm2 than p53 in unstressed cells. USP10 however has been shown to be located in the cytoplasm in unstressed cells and deubiquitinates cyptoplasmic p53, reversing Mdm2 ubiquitination. Following DNA damage, USP10 translocates to the nucleus and contributes to p53 stability. Also USP10 does not interact with Mdm2. Phosphorylation of the N-terminal end of p53 by the above-mentioned protein kinases disrupts Mdm2-binding. Other proteins, such as Pin1, are then recruited to p53 and induce a conformational change in p53, which prevents Mdm2-binding even more. Phosphorylation also allows for binding of transcriptional coactivators, like p300 or PCAF, which then acetylate the carboxy-terminal end of p53, exposing the DNA binding domain of p53, allowing it to activate or repress specific genes. Deacetylase enzymes, such as Sirt1 and Sirt7, can deacetylate p53, leading to an inhibition of apoptosis. Some oncogenes can also stimulate the transcription of proteins that bind to MDM2 and inhibit its activity. Role in disease .]] showing cells with abnormal p53 expression (brown) in a brain tumour. p53 immunostain.]] If the TP53 gene is damaged, tumor suppression is severely reduced. People who inherit only one functional copy of the TP53 gene will most likely develop tumors in early adulthood, a disease known as Li-Fraumeni syndrome. The TP53 gene can also be damaged in cells by mutagens (chemicals, radiation, or viruses), increasing the likelihood that the cell will begin decontrolled division. More than 50 percent of human tumors contain a mutation or deletion of the TP53 gene. Increasing the amount of p53, which may initially seem a good way to treat tumors or prevent them from spreading, is in actuality not a usable method of treatment, since it can cause premature aging. However, restoring endogenous p53 function holds a lot of promise. Loss of p53 creates genomic instability that most often results in the aneuploidy phenotype. Certain pathogens can also affect the p53 protein that the TP53 gene expresses. One such example, human papillomavirus (HPV), encodes a protein, E6, which binds to the p53 protein and inactivates it. This, in synergy with the inactivation of another cell cycle regulator, pRb, by the HPV protein E7, allows for repeated cell division manifested in the clinical disease of warts. Certain HPV types, in particular types 16 and 18, can also lead to progression from a benign wart to low or high-grade cervical dysplasia, which are reversible forms of precancerous lesions. Persistent infection of the cervix over the years can cause irreversible changes leading to carcinoma in situ and eventually invasive cervical cancer. This results from the effects of HPV genes, particularly those encoding E6 and E7, which are the two viral oncoproteins that are preferentially retained and expressed in cervical cancers by integration of the viral DNA into the host genome. In healthy humans, the p53 protein is continually produced and degraded in the cell. The degradation of the p53 protein is, as mentioned, associated with MDM2 binding. In a negative feedback loop, MDM2 is itself induced by the p53 protein. However, mutant p53 proteins often do not induce MDM2, and are thus able to accumulate at very high concentrations. Worse, mutant p53 protein itself can inhibit normal p53 protein levels. In some cases, single missense mutations in p53 have been shown to disrupt p53 stability and function. Experimental analysis of p53 mutations Most p53 mutations are detected by DNA sequencing. However, it is known that single missense mutations can have a large spectrum from rather mild to very severe functional effects. Discovery p53 was identified in 1979 by Lionel Crawford, David P. Lane, Arnold Levine, and Lloyd Old, working at Imperial Cancer Research Fund (UK) Princeton University/UMDNJ (Cancer Institute of New Jersey), and Sloan-Kettering Memorial Hospital, respectively. It had been hypothesized to exist before as the target of the SV40 virus, a strain that induced development of tumors. The TP53 gene from the mouse was first cloned by Peter Chumakov of the Russian Academy of Sciences in 1982, and independently in 1983 by Moshe Oren in collaboration with David Givol (Weizmann Institute of Science). The human TP53 gene was cloned in 1984 and the full length clone in 1985. It was initially presumed to be an oncogene due to the use of mutated cDNA following purification of tumour cell mRNA. Its character as a tumor suppressor gene was finally revealed in 1989 by Bert Vogelstein working at Johns Hopkins School of Medicine. Warren Maltzman, of the Waksman Institute of Rutgers University first demonstrated that TP53 was responsive to DNA damage in the form of ultraviolet radiation. In a series of publications in 1991-92, Michael Kastan, Johns Hopkins University, reported that TP53 was a critical part of a signal transduction pathway that helped cells respond to DNA damage. In 1992, Wafik El-Deiry when he was working with Bert Vogelstein at Johns Hopkins University identified the consensus sequence, to which human p53 could bind, by immunoprecipitating human genomic DNA that could be bound by baculovirus-produced human p53 protein. This sequence was published in the first issue of the journal Nature Genetics in 1992 in work that is highly cited. The consensus sequence is 5'-RRRCWWGYYY-N(0-13)-RRRCWWGYYY-3' and is located in the regulatory regions of genes that are activated by the p53 transcription factor. The presence of p53 response elements in or around genes (promoters, upstream sequences, introns) is a powerful predictor of regulation and activation of a particular gene by p53. In 1993, p53 was voted molecule of the year by Science magazine. That same year, 1993, Wafik El-Deiry when he was working with Bert Vogelstein at Johns Hopkins University discovered p21(WAF1) as a gene regulated directly by p53. This work was reported in the most highly cited paper ever published in the journal Cell, and provided a molecular mechanism by which mammalian cells undergo growth arrest when damaged. The p21(WAF1) protein binds directly to cyclin-CDK complexes that drive forward the cell cycle and inhibits their kinase activity thereby causing cell cycle arrest to allow repair to take place. p21 can also mediate growth arrest associated with differentiation and a more permanent growth arrest associated with cellular senescence. The p21 gene contains several p53 response elements that mediate direct binding of the p53 protein, resulting in transcriptional activation of the gene encoding the p21(WAF1) protein. Interactions p53 has been shown to interact with: * AIMP2, * ANKRD2, * APTX, * ATM, * ATR, * ATF3, * AURKA, * BAK1, * BARD1, * BLM, * BRCA1, * BRCA2, * BRCC3, * BRE, * CEBPZ, * CDC14A, * Cdk1, * CFLAR, * CHEK1, * CCNG1, * CREBBP, * CREB1, * Cyclin H, * CDK7, * DNA-PKcs, * E4F1, * EFEMP2, * EIF2AK2, * ELL, * EP300, * ERCC6, * GNL3, * GPS2, * GSK3B, * HSP90AA1, * HIF1A, * HIPK1, * HIPK2, * HMGB1, * HSPA9, * Huntingtin, * ING1, * ING4, * ING5, * IκBα, * KPNB1, * LMO3, * Mdm2, * MDM4, * MED1, * MAPK9, * MNAT1, * NDN, * NCL, * NUMB, * NF-κB, * P16, * PARC, * PARP1, * PIAS1, * CDC14B, * PIN1, * PLAGL1, * PLK3, * PRKRA, * PHB, * PML, * PSME3, * PTEN, * PTK2, * PTTG1, * RAD51, * RCHY1, * RELA, * RPA1, * RPL11, * S100B, * SUMO1, * SMARCA4, * SMARCB1, * SMN1, * STAT3, * TBP, * TFAP2A, * TFDP1, * TIGAR, * TOP1, * TOP2A, * TP53BP1, * TP53BP2, * TOP2B, * TP53INP1, * TSG101, * UBE2A, * UBE2I, * UBC, * USP7, * WRN, * WWOX, * XPB, * YBX1, *YPEL3, * YWHAZ, * Zif268, * ZNF148, Interactive pathway map References External links * * GeneReviews/NCBI/NIH/UW entry on Li-Fraumeni Syndrome * TUMOR PROTEIN p53 @ OMIM * p53 @ The Atlas of Genetics and Cytogenetics in Oncology and Haematology * TP53 Gene @ GeneCards * p53 News provided by insciences organisation * * * The George Pantziarka TP53 Trust A support group from the UK for sufferers of Li-Fraumeni Syndrome or other TP53-related disorders * IARC TP53 Somatic Mutations database maintained at IARC, Lyon, by Magali Olivier Category:Programmed cell death Category:Proteins Category:Transcription factors Category:Tumor suppressor genes Category:Apoptosis Category:Genes mutated in mice Category:Aging-related proteins ar:بي53 ca:P53 cs:P53 de:P53 et:P53 es:P53 fa:پی۵۳ fr:P53 ko:P53 id:P53 it:P53 he:P53 lt:P53 hu:P53 ja:P53遺伝子 pl:P53 pt:P53 ru:P53 sl:P53 fi:P53 th:P53 tr:P53 uk:P53 ur:پی 53 (لحمیہ) vi:P53 zh:P53